1,720,980 research outputs found
How surface and textural properties affect the behaviour of Mn-based catalysts during transesterification reaction to produce biodiesel
No full textThis work was aimed at investigating the catalytic behaviour of MnCeOx and MnZrOx systems in biodiesel production by sunflower oil transesterification reaction with methanol. Surface and textural properties were deeply investigated by different techniques whereas CH3OH surface reactivity was evaluated by FT-IR and MeOH-TPSR measurements, in order to disclose the nature of the active sites and to provide evidences of a complex reaction mechanism, in which a synergic role of Mn and carrier significantly affects the methyl esters productivity. Direct relationship among catalytic activity, density of strong basic sites and amount of adsorbed bidentate methoxy species were found. The doubly-bridging coordinated methoxy species were recognized as the ones mainly involved in the transesterification reaction. Anyway, even if the basic strength resulted to be considered the key factor for MeOH activation, only the proper balance between basic and acid sites controls catalyst behaviour. The linear dependence of activity with catalyst porosity clearly demonstrated that a wide porous structure is required to enhance the sites accessibility to large triglycerides (TGs) molecules
Highly effective MnCeOx catalysts for biodiesel production by transesterification of vegetable oils with methanol
No full textThis paper reports the results obtained using a novel MnCeOx system in the transesterification reaction
of refined sunflower oil with methanol. The performance of such catalysts has been compared with that
of common acid supported catalysts. Results obtained revealed that MnCeOx system possesses a superior
activity especially by operating at low temperatures (≤120 ◦C). Independently of Mn loading, the redox precipitation
method for the preparation of Mn-based systems allowed to obtain always high dispersed
catalysts and, as a consequence, a linear relationship between reaction rate and Mn loading was obtained.
NH3-TPD and CO2-TPD measurements indicate that MnCeOx systems are characterized by a prevalent
nature of basic sites. However, the catalyst performance is the result of a synergic role played by both
the surface acid/base character and textural porosit
Dimethyl ether as circular hydrogen carrier: Catalytic aspects of hydrogenation/dehydrogenation steps
No full textThe intermittent nature of renewable resources requires for most applications the development of efficient and cost-effective technologies for steady supply of electrical energy. The storage of energy in the form of hydrogen chemically bound within organic molecules (rather than physically as compressed gas or cooled liquid) represents an alternative approach that is attracting great research interest. Compared to other liquid organic hydrogen carriers (LOHCs), dimethyl ether (DME) appears to have the largest potential impact on society, especially if inserted in technological chains of CO2 sequestration and utilization, so to determine an effective mitigation of environmental issues, without any net effect on the carbon footprint. Specifically, the steps of H2 storage and H2 release can take place in two coupled chemical processes, constituted by the exothermic synthesis of DME via CO2 hydrogenation and the endothermic steam reforming of DME, respectively. Herein, the latest advances in the development of heterogeneous bifunctional and hybrid catalysts for the direct hydrogenation of CO2 to DME are thoroughly reviewed, with special emphasis on thermodynamics, catalyst design and process feasibility. Despite many aspects behind the mechanism of DME synthesis from H2-CO2 streams are still to be uncovered, the recent progress in the research on H2 release by DME steam reforming is increasing the interest for effectively closing this binary H2 loop, in view of future green deals and sustainable research developments
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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